The long term objective of this research is to define the molecular basis of the defects that are responsible for the pharmacogenetic syndrome Malignant Hyperthermia (MH). In this anesthetic reaction that occurs in susceptible individuals during surgery, certain anesthetic agents and depolarizing muscle relaxants trigger a rise in body temperature and muscle rigidity. Using a purebred strain of MH susceptible (MHS) Pietrain pigs, it has been demonstrated that the altered control of sarcoplasmic Ca2+ in MHS in skeletal muscle likely results from specific defects in the sarcoplasmic reticulum (SR) and transverse tubule (TT) membranes. The first hypothesis to be tested in this project is that an abnormality in the SR calcium release channel/ryanodine receptor (Ca/RyR) is responsible for the abnormal calcium regulation in MHS muscle. To this end, rapid calcium release from calcium-filled MHS and normal SR vesicles will be examined. These results will be correlated with both the binding of the high affinity ligand ryanodine, and the single channel kinetics of the Ca/RyR to define the defect in the MHS SR Ca/RyR. The second hypothesis to be tested in this study is that an altered TT dihydropyridine (DHP) receptor contributes to the abnormal sarcoplasmic Ca regulation in MH muscle. It will be determined whether the decreased Bmax for DHP binding to MHS TT is due either to a decreased content of the receptor protein in MHS TT, or to a defect in the DHP receptor of MHS TT such that its regulation of excitation-contraction coupling is altered in MHS muscle. Should these data indicated an altered conformation of the DHP receptor in MHS TT, the single calcium channel kinetics of this receptor in the two types of TT will be characterized. Since volatile anesthetics and dantrolene (which blocks the MH response) may interact with both SR Ca/RyR and the TT DHP receptor, it will also be appropriate to examine the effect of these agents on the single calcium channel kinetics of these two components in MHS and normal TT membranes. An understanding of the nature of MH will be of great assistance in the future identification, management and treatment of MHS individuals; will provide basic information regarding the protein complexes that effect excitation-contraction in normal skeletal muscle; and will be important in the future elucidation of the etiology of many other muscle diseases in which excitation-contraction or calcium regulation is abnormal.